Impingement of acetabular cups in a hip simulator: comparison of highly cross-linked and conventional polyethylene.

We hypothesized that the reduction in toughness that accompanies elevated levels of cross-linking in ultrahigh-molecular weight polyethylene would lead to increased wear and damage in acetabular cups under conditions of impingement with the neck of the femoral component. Test cups were exposed to 2.8, 10, and 20 Mrad of gamma irradiation and were tested in a simulator, incorporating impingement during every wear cycle. Wear behavior was compared based on wear rate, observations of damage, and the number and morphology of wear particles. The 10-Mrad cups had the lowest rate (15.2 +/- 5.1 mg/Mc), followed by the 2.8-Mrad (40.1 +/- 4.2 mg/Mc) and 20-Mrad (67.9 +/- 24.2 mg/Mc) groups. The wear damage was most severe in the 20-Mrad cups, although all 3 groups showed pitting and delaminating. Wear rates and damage of highly cross-linked polyethylene cups were significantly higher in an impingement wear test than in previous simulator studies.